Utility vehicles and vans with liftgates that are hinged at the top about a generally horizontal axis are used by large numbers of people today. Some of these liftgates are large and heavy. Their size and weight make some liftgates difficult to open and close. Some of the liftgates are also a great distance above the ground when they are fully opened. Their height above the ground makes them very difficult for some people to close. For these and other reasons many people would like to have a power operating system for opening and closing the liftgate.
Liftgates that have two or more gas springs for a counter balance system are common. See for instance U.S. Pat. No. 5,448,856 granted to Thomas S. Moore et al Sep. 12, 1995; U.S. Pat. No. 5,531,498 granted to David J. Kowall Jul. 2, 1996; and U.S. Pat. No. 5,588,258 granted to Kevin Wright et al Dec. 1, 1996. Gas springs in such counter balance systems generally occupy a position in which their axis is substantially parallel to the closed liftgate so that the gas springs are hidden when the liftgate is closed. In this closed position the moment arm of the gas springs is quite small. With such counterbalance systems the lift gate must be opened about one-third of the way with either manual or power assistance before the gas springs exert sufficient force to open the liftgate without the manual or power assistance.
There are even some counterbalance systems in which the gas springs pass over center and bias a liftgate toward a closed position when the liftgate is closed. With these self locking counterbalance systems, the liftgate may need to be opened more than one-third of the way before the gas springs will open the liftgate without manual or power assistance.